Maybe they already started on it, but their hands are full at the time being with so many games in progress between 2014 and 2015.

They've probably been working on Animal Crossing since New Leaf came out in Japan. Not so sure about Wii Sports Resort, though. They'd probably prefer to make a game that would sell better.

I think you underestimate how well a gamepad/QoL/Wii Fit U-infused Wii Sports Resort could sell!

For few members of my family, it's pretty much the only game they play...

IMO -- every franchise they've shown in Nintendoland is one they play to deliver on WiiU. Not so sure about SSB stages though

Uh, not right. Compared to making a game designing the 3D models for these background worlds is nothing. Also, the models also have probably cut a lot of corners, may not be in correct proportions for a game, and probably have poor textures as their simply so far away and not the main draw of this game. Not to mention those background models probably don't have any interactive properties.

To say they could just slap Animal Crossing on WiiU no problem right now is kinda equivalent to me 3D modeling that (not too complicated looking) town in Maya or Unity or something and saying I'm well on my way to having an Animal Crossing game.

We're talking about an under 2% head start on each of these games if they could and even wanted to use these world designs.

This is exactly how I feel when I'm playing MK8. So many of those levels would be fun to run/jump in as mario or whoever. I'm hoping for some "get out of the kart and walk" DLC...but we all know that would never happen.